In recent years, there have been proposed distributed printing techniques in order to process a large amount of print jobs in an office having plural image forming apparatuses. Further, in order to reduce effort of sorting operations under the condition that a large amount of sets of printed materials were made, there has been used an image forming apparatus having a paper-shift function. This paper-shift function is a function of ejecting sheets of paper so as to stack up the sheets one by one with the sheets shifted in alternate directions perpendicular to the paper ejecting direction, which is effective for the situation that the ejected outputs are separately distributed to people.
As an example of a paper-shift function, JP-A No. H11-116129 discloses a printing apparatus having the following structure. The printing apparatus includes plural paper-ejection slots for ejecting printed recording media, and a paper-ejecting unit for ejecting recording media to any one of the paper ejection slots, wherein on the recording media, printing is performed based on image information transmitted from an information processing apparatus through a prescribed communication medium. The printing apparatus further includes a paper-shift unit for performing paper-shift ejection to shift the position where recording medium ejected from the paper ejecting unit is put, in a predetermined direction. The printing apparatus further includes a first judging unit, a storing unit, a second judging unit and a control unit. The first judging unit judges whether the paper-shift ejection has been set in an outputting job or not. The storing unit stores the condition of paper-shift ejection of each paper-ejection slot. The second judging unit judges whether a recording medium which has been outputted under the paper-shift ejection is placed on each of the paper-ejecting slots or not, based on the condition of paper-shift ejection in each paper-ejection slot, which has been stored in the storing unit. The control unit controls the paper-ejection to eject an output of a job in which paper-shift ejection has been set and an output of a job in which paper-shift ejection has not been set, separately to different paper-ejection slots, based on the judging results of the first judging unit and the second judging unit.
However, when the distributed printing is carried out with plural image forming apparatuses each having a paper-shift function, there can be caused a situation that sheets of paper are the same in size but are different in their orientation and it makes piling up the gathered sets of paper sheets difficult. Further, there can be caused a situation that piling up the gathered sets of paper sheets makes the boundary of the sets unclear in case that the last-printed set of paper sheets in one image forming apparatus and the first-printed set of paper sheets in another image forming apparatus are shifted in the same direction.